Disk I/O Tuning

Chapter 3: ATA Tuning in LINUX

with a chosen set of
configuration settings. In practice, all that is typically
necessary to test a configuration (prior to using k) is to
verify the drive can be read/written, and no error logs (kernel
messages) are generated in the process (look in /var/adm/messages
on most systems)

-K

- Set the drive's keep_features_over_reset flag. Setting
this enables the drive to retain the settings for -APSWXZ over a
soft reset (as done during the error recovery sequence). Not
all drives support this feature.

-m

- Get/set sector count for multiple sector I/O on the drive. A
setting of 0 disables this feature. Multiple sector mode ( IDE
Block Mode) is a feature of most modern IDE hard drives,
permitting the transfer of multiple sectors per I/O interrupt,
rather than the usual one sector per interrupt. When this
feature is enabled, it typically reduces operating system
overhead for disk I/O by 30-50%. On many systems, it also
provides increased data throughput of anywhere from 5% to 50%.
HOWEVER, some drives, most notably the WD Caviar series, seem
to run slower with multiple mode enabled. Your mileage may
vary. Most drives support the minimum settings of 2, 4, 8, or
16 (sectors). Larger settings may also be possible, depending
on the drive. A setting of 16 or 32 seems optimal on many
systems. Western Digital recommends lower settings of 4 to 8 on
many of their drives, due to tiny (32kB) drive buffers and
non-optimized buffering algorithms. The -i flag can be used to
find the maximum setting supported by an installed drive (look
for MaxMultSect in the output). Some drives